This invention relates generally to methods for creating fatigue-resistant and damage-tolerant components, and more specifically, to a method of evaluating tools used to produce such components.
Various metallic, ceramic, and composite components, such as gas turbine engine fan and compressor blades, are susceptible to cracking from fatigue and damage (e.g. from foreign object impacts). This damage reduces the life of the part, requiring repair or replacement. It is known to protect components from crack propagation by inducing residual compressive stresses therein. Methods of imparting these stresses include shot peening, laser shock peening (LSP), pinch peening, and low plasticity burnishing (LPB). These methods are typically employed by applying a “patch” of residual compressive stresses over an area to be protected from crack propagation.
A typical burnishing apparatus includes rolling burnishing elements such as cylinders or spheres which are loaded with a burnishing force by mechanical or hydrostatic pressure. These burnishing processes require physical contact between the burnishing element and the workpiece. Even though lubrication is provided, wear of the burnishing element occurs during normal use and needs to be monitored. The quality of the burnishing relies on the condition of the burnishing element. Worn elements can cause material transfer between the element and the workpiece, which adversely affects the surface finish and residual stresses.
In the prior art, controlling degradation of the burnishing element condition relies on controlling its cumulative burnishing time. Indication of wear is determined with visual inspections of the burnishing element and the workpieces. Steps are also taken to prevent wear, for example by controlling the quality and the quantity of coolant/lubricant used in the burnishing process. However, there is no uniform, efficient test for burnishing element wear.